How to use: 

To bring assets into your scene, just append or link them as a group (in Blender 2,80 - as a collection).

I suggest use append Particle System into your scene (because it's bring object group and its particle settings already in Blender 2,79)

Check this settings before you bring stuff to the scene. Then grass and plant sizes is synchronized with you scene.

in Blender 2.79

in Blender 2.80

If you using Blender 2,79:

Go: File --> Append -->Grass_and_plants_assets_pack_279 --> All_in_one_grass_and_plants_279.blend --> ParticleSettings --> buffalo grass --> Append from Library

Then select your object for the grass (for example plain ) and Go --> Particles --> add particle system  

Then choose Browse Particle Settings to be linked

And then choose buffalo grass

If you using Blender 2,80:

Go: File --> Append -->Grass_and_plants_assets_pack_280 --> All_in_one_grass_and_plants_280.blend --> Collection --> buffalo grass --> Append from Library

Then Go: File --> Append -->Grass_and_plants_assets_pack_280 --> All_in_one_grass_and_plants_280.blend --> ParticleSetings --> buffalo grass --> Append from Library

Then select your object for the grass and Go --> Particles --> add particle system 

Then choose Browse Particle Settings to be linked

Then select buffalo_grass in Collection -- Instance Collection

Almost every grass or plant texture has an orange node with which you can change the green color to a drier color.

I hope this help you and good luck!